Polyphenylene sulfide fiber and nonwoven fabric

ABSTRACT

Provided are a polyphenylene sulfide fiber including a PPS resin as a main component and having both excellent heat resistance and excellent thermal bonding properties, and a nonwoven fabric including the fiber. The polyphenylene sulfide fiber includes polyphenylene sulfide as a main component and having the sum of the crystallinity and the rigid amorphous fraction of 30% to 90%. The crystallinity is preferably not less than 5% and less than 25%. The polyphenylene sulfide fiber is used to form a nonwoven fabric. The nonwoven fabric is preferably produced by consolidation by thermal bonding or mechanical entanglement.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Phase application of PCT/JP2012/064256, filedJun. 1, 2012, which claims priority to Japanese Patent Application No.2011-123994, filed Jun. 2, 2011, the disclosures of these applicationsbeing incorporated herein by reference in their entireties for allpurposes.

FIELD OF THE INVENTION

The present invention relates to a fiber comprising a resin comprisingpolyphenylene sulfide (hereinafter sometimes abbreviated to “PPS”) as amain component, and a nonwoven fabric comprising the fiber.

BACKGROUND OF THE INVENTION

PPS resins are excellent in heat resistance, flame retardancy andchemical resistance and are therefore suitably used as engineeringplastics, films, fibers, nonwoven fabrics, or the like. Especiallynonwoven fabrics utilizing these excellent properties are expected to beused in industrial applications such as heat-resistant filters,electrical insulation materials, and battery separators.

However, in cases where a PPS resin is spun into fibers to form anonwoven fabric, problems may arise concerning poor thermal dimensionalstability, which may lead to significant thermal shrinkage of the fibersor the nonwoven fabric.

In order to improve the dimensional stability of PPS nonwoven fabrics,there has been proposed, for example, a filament nonwoven fabricproduced by spun bonding in which a PPS resin is spun and drawn intofilaments, the filaments are temporarily bonded at a temperature notmore than the first crystallization temperature of the fabric to beproduced, the obtained fabric is subjected to heat treatment understrain at a temperature not less than the first crystallizationtemperature to promote the crystallization of the filaments, and thefabric is subjected to permanent bonding (see, for example, PatentLiterature 1). There has also been proposed a heat-resistant nonwovenfabric produced by spinning and drawing a PPS resin at a high spinningspeed of 6,000 m/min or more to promote the crystallization of thefibers, and thereby to suppress thermal shrinkage (see, for example,Patent Literature 2). These proposals, however, suffer from poor thermalbonding properties.

Thus there has been no proposal for a PPS fiber or PPS nonwoven fabrichaving both heat resistance and thermal bonding properties.

PATENT LITERATURE

Patent Literature 1: JP-2008-223209 A

Patent Literature 2: WO 2008/035775

SUMMARY OF THE INVENTION

In consideration of the above problems in the conventional art, thepresent invention aims to provide a fiber comprising a PPS resin as amain component and having both excellent heat resistance and excellentthermal bonding properties, and a nonwoven fabric comprising the fiber.

The reason conventional techniques as described above cannot achieveheat resistance and thermal bonding properties at the same time isprobably that promotion of crystallization leads to increase in thethermal dimensional stability on the one hand and, on the other hand, todecrease in the amorphous phase, which can melt and contribute tothermal bonding. The inventors conducted intensive research tosimultaneously achieve the above properties that seem incompatible and,as a result, found the following means.

That is, a first aspect of the present invention relates to apolyphenylene sulfide fiber comprising polyphenylene sulfide as a maincomponent and having the sum of the crystallinity and the rigidamorphous fraction of 30% to 90%.

A second aspect of the present invention relates to a nonwoven fabriccomprising the polyphenylene sulfide fiber according to the first aspectof the present invention.

The polyphenylene sulfide fiber (hereinafter also referred to as PPSfiber) of the first aspect of the present invention having the sum ofthe crystallinity and the rigid amorphous fraction of 30% or more,preferably 35% or more, is excellent in thermal dimensional stability.The polyphenylene sulfide fiber having the sum of the crystallinity andthe rigid amorphous fraction of 90% or less, more preferably 70% orless, still more preferably 50% or less, is preferred in terms ofthermal bonding properties.

The crystallinity is not limited to a specific range. However, thecrystallinity is preferably 5% or more, more preferably 10% or more, andstill more preferably 15% or more. When a nonwoven web of the fiberhaving such crystallinity is thermally bonded, the resulting sheet isprevented from breakage due to being wound up around a roll. Thecrystallinity is preferably less than 25%, more preferably 23% or less,and still more preferably 20% or less so that a large amount of theamorphous phase (including the rigid amorphous fraction) is present inthe fiber and contributes to excellent thermal bonding properties forthermal bonding of the nonwoven web.

As regards the above-mentioned nonwoven fabric, a production methodtherefor and the structure thereof are not particularly limited. Forexample, the nonwoven fabric can be produced by spun bonding in whichthe PPS fibers are consolidated by thermal bonding or mechanicalentanglement.

The PPS fiber of the present invention has excellent thermal bondingproperties while maintaining the properties of a PPS resin, namely, heatresistance, chemical resistance, and flame retardancy. Consequently, thenonwoven fabric of the present invention also has excellent mechanicalstrength while maintaining the properties of a PPS resin, namely, heatresistance, chemical resistance, and flame retardancy and is thereforeusable for various industrial applications.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the relation of the boiling water shrinkage tothe crystallinity in PPS fibers.

FIG. 2 is a graph showing the relation of the boiling water shrinkage tothe sum of the crystallinity and the rigid amorphous fraction in PPSfibers.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The resin used in the present invention comprises PPS as a maincomponent. Hereinafter, the resin that is used in the present inventionand comprises PPS is also referred to as the “PPS resin”.

PPS is a polymer having, as the repeating unit, a phenylene sulfide unitsuch as a p-phenylene sulfide unit and a m-phenylene sulfide unit.Preferred is a substantially linear polymer containing 90 mol % or moreof a p-phenylene sulfide unit because of its heat resistance andspinnability. In cases where PPS is used as a main component to obtain apolymer with a low melting point, preparation of a polymer bycopolymerization of a p-phenylene sulfide unit with a m-phenylenesulfide unit is preferred in that the flame retardancy and chemicalresistance of PPS are not impaired. The copolymerized PPS can besuitably used as a component for a composite fiber.

Preferably, PPS is substantially not copolymerized withtrichlorobenzene. This is because trichlorobenzene has three or morehalogen substituents per benzene ring and thus the copolymerization ofPPS with trichlorobenzene results in a branched structure, leading topoor spinnability of the resulting PPS resin and frequent breakage ofthe resulting fibers during spinning and drawing. The copolymerizedtrichlorobenzene content, as the degree of being substantially free fromcopolymerized trichlorobenzene, is preferably 0.05 mol % or less, andmore preferably 0.01 mol % or less.

The PPS content of the PPS resin is preferably 85% by mass or more, morepreferably 90% by mass or more, and still more preferably 95% by mass ormore in view of heat resistance, chemical resistance, and the like. Tothe PPS resin may be added a nucleator, a matting agent, a pigment, anantifungal agent, an antibacterial agent, a flame retardant, ahydrophilic agent, and/or the like to the extent that these do notimpair the effects of the present invention.

The PPS resin used in the present invention preferably has a melt flowrate (hereinafter sometimes abbreviated to MFR) measured in accordancewith ASTM D1238-70 (measurement temperature: 315.5° C., measurementload: 5 kg) of 100 to 300 g/10 min. The PPS resin having an MFR of 100g/10 min or more, more preferably 140 g/10 min or more, has moderatefluidity, which contributes to the suppression of increase in the backpressure of the spinneret during melt spinning and to the prevention ofbreakage of the resulting fibers during pulling and drawing. The PPSresin having an MFR of 300 g/10 min or less, more preferably 225 g/10min or less, has a moderately high polymerization degree or molecularweight, which contributes to increase in strength and heat resistancesufficient for practical use.

It is preferred for the PPS fiber of the present invention to have thesum of the crystallinity and the rigid amorphous fraction of 30% to 90%.

The crystallinity herein refers to those determined by measuring with adifferential scanning calorimetry (DSC) as described later in Examples.

The rigid amorphous fraction herein refers to the remainder left aftersubtraction of the crystallinity [%] and the mobile amorphous fraction[%] from the total of the crystal and amorphous fractions (100%) thatconstitutes the fiber, as shown in the following formula:

Rigid amorphous fraction [%]=100[%]−crystallinity [%]−mobile amorphousfraction [%].

The mobile amorphous fraction herein refers to those determined bymeasuring with a temperature modulated DSC as described later inExamples.

The inventors found that not only the crystal fraction but also therigid amorphous fraction significantly affects the thermal dimensionalstability.

That is, as shown in the relation of the boiling water shrinkage to thecrystallinity in FIG. 1, even though the crystallinity values aresubstantially the same among the samples having a crystallinity of lessthan 20%, the boiling water shrinkage greatly varies; however, as shownin the relation of the boiling water shrinkage to the sum of thecrystallinity and the rigid amorphous fraction in FIG. 2, when the rigidamorphous fraction is used as an evaluation factor in addition to thecrystallinity, a strong correlation is observed, which reveals that therigid amorphous fraction significantly affects the thermal dimensionalstability. Although the mechanism is unclear, the rigid amorphousfraction is an amorphous yet is considered to play a similar role tothat of the crystal fraction for the thermal dimensional stability.

In FIGS. 1 and 2, the data is based on Examples and Comparative Examplesdescribed later, and the numbers within the brackets in the graphscorrespond to the numbers in Table 1 described later.

As shown in FIG. 2, the boiling water shrinkage is less than 20% whenthe sum of the crystallinity and the rigid amorphous fraction is 30% ormore, and the boiling water shrinkage is less than 10% when the sum ofthe crystallinity and the rigid amorphous fraction is 35% or more.

In view of suppression of shrinkage in width, wrinkles, and surfaceirregularity caused by thermal shrinkage, the boiling water shrinkage ispreferably 20% or less, more preferably 15% or less, and still morepreferably 10% or less. Consequently, a fiber having the sum of thecrystallinity and the rigid amorphous fraction of 30% or more,preferably 35% or more, has excellent thermal dimensional stability.

In view of thermal bonding properties, in addition to the rigidamorphous fraction, preferably the mobile amorphous fraction is alsocontained in an amount of 10% or more, more preferably 30% or more,still more preferably 50% or more. Although the mechanism is unclear, itis considered that, in thermal bonding, fibers comprising a certainamount of the mobile amorphous fraction more easily undergo plasticdeformation in accordance with the magnitude of the pressure applied tothe fibers for bonding. That is, the sum of the crystallinity and therigid amorphous fraction in the PPS fiber is preferably 90% or less,more preferably 70% or less, and still more preferably 50% or less.

The crystallinity of the PPS fiber of the present invention ispreferably not less than 5% and less than 25%.

As described in the above Patent Literature 2, it has been consideredthat the crystallinity needs to be 25% or more to stably impart thermaldimensional stability to a PPS fiber. However, according to the presentinvention, even when the crystallinity is less than 25%, thermalshrinkage of a PPS fiber can be reduced by increasing the amount of therigid amorphous fraction. Conventionally, low crystallinity of a PPSfiber means the presence of a large amount of the amorphous phase, whichresults in poor thermal dimensional stability; whereas highcrystallinity of a PPS fiber means the presence of a small amount of theamorphous phase, which results in poor thermal bonding properties.According to the present invention, the amorphous phase, especially therigid amorphous fraction, is increased to impart thermal dimensionalstability, thereby achieving both excellent thermal dimensionalstability and excellent thermal bonding properties.

The crystallinity of the PPS fiber of the present invention ispreferably 5% or more, more preferably 10% or more, and still morepreferably 15% or more. When a nonwoven web of the fiber having suchcrystallinity is thermally bonded, the resulting sheet is prevented frombreakage due to being wound up around a roll. The crystallinity is lessthan 25%, more preferably 23% or less, and still more preferably 20% orless so that a large amount of the amorphous phase (including the rigidamorphous fraction) is present in the fiber and contributes to excellentthermal bonding properties for thermal bonding of the nonwoven web.

The cross section of the PPS fiber of the present invention may be anyshape such as a circular shape, a hollow round shape, an oval shape, aflat shape, a polygonal shape, and a multilobal shape (such as an Xshape and a Y shape).

The PPS fiber of the present invention may be in a composite form.Examples of the composite form include a core-sheath type, an eccentriccore-sheath type, an Umishima type, a parallel type, a radial type, anda multilobal type. Among these, preferred is a core-sheath type, whichis suitable for achieving excellent spinnability.

The average single fiber fineness of the PPS fiber of the presentinvention is preferably 0.5 to 10 dtex.

When spinning is performed so as to form fibers having an average singlefiber fineness of 0.5 dtex or more, more preferably 1 dtex or more,still more preferably 2 dtex or more, spinnability of the fibers isassured and frequent breakage of the fibers during spinning can beprevented.

When spinning is performed so as to form fibers having an average singlefiber fineness of 10 dtex or less, more preferably dtex or less, stillmore preferably 4 dtex or less, the discharge rate of a molten resin perhole of a spinneret' can be suitably reduced to allow the resultingfibers to sufficiently cool down, thereby preventing reduction inspinnability due to fusion bonding between the fibers. Moreover, whensuch fibers are formed into a nonwoven fabric, the variation in the massper unit area of the nonwoven fabric can be reduced, thereby providingexcellent quality for the surfaces of the nonwoven fabric. Also in viewof the dust collecting performance of the nonwoven fabric used as afilter or the like, the average single fiber fineness is preferably 10dtex or less, more preferably 5 dtex or less, and still more preferably4 dtex or less.

The PPS fiber of the present invention can be used as a fiber forforming any type of fabric such as woven fabrics and nonwoven fabricsbut, because of its excellent thermal bonding properties, the PPS fiberof the present invention can be more suitably used as a component fiberof a nonwoven fabric whose structure is fixed by thermal press-bonding.

The PPS nonwoven fabric of the present invention may be a filamentnonwoven fabric or a staple nonwoven fabric, but a filament nonwovenfabric produced by spun bonding is preferred for its excellentproductivity.

The mass per unit area of the nonwoven fabric of the present inventionis preferably 10 to 1000 g/m². The nonwoven fabric having a mass perunit area of 10 g/m² or more, more preferably 100 g/m² or more, stillmore preferably 200 g/m² or more, exhibits a sufficient mechanicalstrength for practical use. In cases where the nonwoven fabric is usedas a filter or the like, the mass per unit area is 1000 g/m² or less,more preferably 700 g/m² or less, and still more preferably 500 g/m² orless. The nonwoven fabric having such a mass per unit area has moderateair permeability and thus prevents pressure loss from increasing.

The thermal shrinkage rate at 200° C. of the PPS nonwoven fabric of thepresent invention is preferably 5% or less both in the longitudinal andtransverse directions. Because of its properties, PPS nonwoven fabricsare often used under high temperature. When the thermal shrinkage rateat 200° C. of the PPS nonwoven fabric of the present invention ispreferably 5% or less, more preferably 3% or less, reduction in itsperformance due to dimensional change can be prevented, and such a PPSnonwoven fabric is suitable for practical use.

The PPS nonwoven fabric of the present invention preferably has alongitudinal tensile strength retention rate measured by a heat-exposureresistance test in the air at 210° C. for 1500 hours of 80% or more. ThePPS nonwoven fabric having a longitudinal tensile strength retentionrate of 80% or more, more preferably 85% or more, still more preferably90% or more, can be used as a heat-resistant filter or the like that isused under high temperature for a long period of time. The upper limitvalue of the longitudinal tensile strength retention rate is notparticularly limited but is preferably 150% or less.

Next, a production method for a PPS nonwoven fabric by spun bonding,which is a preferred embodiment for the PPS fiber and PPS nonwovenfabric of the present invention, will be described below.

Spun bonding is a production method that requires the steps of: meltinga resin, spinning the molten resin from a spinneret, solidifying theresulting filamentary streams by cooling, pulling and drawing thefilamentary streams by means of an ejector, collecting the filaments ona moving net to form a nonwoven web, and consolidating the nonwoven webby thermal bonding or mechanical entanglement.

The spinneret and the ejector may be in various shapes such as acircular shape and a rectangular shape. Inter alia, a combination of arectangular spinneret and a rectangular ejector is preferred because theamount of compressed air to be used is relatively small and thefilaments are hardly fusion-bonded or scratch each other.

The spinning temperature for melting and spinning PPS is preferably 290to 380° C., more preferably 295 to 360° C., and still more preferably300 to 340° C. The spinning temperature within the above range allowsPPS to be brought into a stable molten state and to exhibit excellentspinning stability.

Examples of the method for cooling the spun filamentary streams include,for example, a method in which cold air is forced to blow over thefilamentary streams, a method in which the filamentary streams areallowed to cool down at atmospheric temperature around the filamentarystreams, a method in which the distance between the spinneret and theejector is adjusted, and a combination thereof. The cooling conditionscan be appropriately adjusted and adopted in consideration of thedischarge rate per hole of the spinneret, the spinning temperature, theatmospheric temperature, and the like.

Next, the filamentary streams that have solidified by cooling are pulledand drawn by compressed air blown from the ejector. The method forpulling and drawing the filamentary streams by means of the ejector andthe conditions therefor are not particularly limited, but a method inwhich the filamentary streams are pulled and drawn by compressed airheated and blown from the ejector, the compressed air being heated to100° C. or more, preferably 140° C. or more, more preferably 180° C. ormore, is preferred in that the crystallization of the PPS fiber issuppressed and at the same time the rigid amorphous fraction isincreased. Since heated compressed air is used, the filamentary streamsthat are being pulled and drawn are simultaneously heat treated.However, the heat treatment duration is extremely short and thereforethe rigid amorphous fraction, which is an intermediate phase between thecrystal phase and the amorphous phase, can be specifically increased.The upper limit of the temperature of the heated compressed air is notmore than the melting point of PPS.

Another method for heat treating the filamentary streams during pullingand drawing include a method in which a heater is disposed before orafter the ejector. However, this method is not preferred because thethermal conductivity is inferior to that in the above method in which ahot air of high temperature is directly blown over the fibers, andconsequently the heat does not contribute to increase in the rigidamorphous fraction.

The spinning speed is preferably not less than 3,000 m/min and less than6,000 m/min. Spinning at a spinning speed of 3,000 m/min or more, morepreferably 3,500 m/min or more, still more preferably 4,000 m/min ormore, can produce a PPS fiber having high crystallinity. Consequently,when a resulting nonwoven web is thermally bonded, the resulting sheetis prevented from breakage due to being wound up around a roll. Spinningat a spinning speed less than 6,000 m/min is preferred because excessiveincrease in the crystallinity can be prevented and excellent spinningstability can be achieved.

Next, the PPS fibers obtained by drawing are collected on a moving netto form a nonwoven web, and the obtained nonwoven web is consolidated bythermal bonding or mechanical entanglement to form a nonwoven fabric.

Preferred method for consolidation into a nonwoven fabric are a thermalbonding method in which thermal press-bonding is performed using varioustypes of rolls such as a roll pair for thermal embossing that iscomposed of upper and lower rolls each having embossment on theirsurfaces, a roll pair for thermal embossing that is composed of a rollhaving a flat (smooth) surface and a roll having embossment on itssurface, or a roll pair for thermal calendering that is composed ofupper and lower flat (smooth) rolls; and a mechanical entanglementmethod using needle punching or water jet punching.

In cases where thermal press-bonding is performed with a thermalembossing roll pair, the embossment pattern on the embossing roll(s) maybe circle, oval, square, rectangle, parallelogram, diamond, regularhexagon, or regular octagon, or the like.

The surface temperature of the thermal embossing roll pair is preferably5 to 30° C. lower than the melting point of PPS. By means of the thermalembossing roll pair having a surface temperature not lower than thetemperature that is 30° C. lower than the melting point of PPS, morepreferably a surface temperature not lower than the temperature that is25° C. lower than the melting point of PPS, still more preferably asurface temperature not lower than the temperature that is 20° C. lowerthan the melting point of PPS, the nonwoven web is thermally bonded to asufficient extent and thereby flaking off and fluffing of the resultingnonwoven fabric can be prevented. By means of the thermal embossing rollpair having a surface temperature not higher than the temperature thatis 5° C. lower than the melting point of PPS, perforation in thepress-bonded parts due to fusion of the fibers can be prevented.

The linear pressure applied by the thermal embossing roll pair duringthermal bonding is preferably 200 to 1500 N/cm. By means of the rollswith a linear pressure of 200 N/cm or more, more preferably 300 N/cm ormore, the nonwoven web is thermally bonded to a sufficient extent andthereby flaking off and fluffing of the resulting sheet can beprevented. By means of the rolls with a linear pressure of 1500 N/cm orless, more preferably 1000 N/cm or less, the raised portions of theembossment are prevented from biting into the nonwoven fabric andthereby trouble removing the nonwoven fabric from the rolls or thebreakage of the nonwoven fabric can be prevented.

The bonding area provided by means of the thermal embossing roll pair ispreferably 8 to 40%. Thermal bonding with the roll pair so as to providea bonding area of 8% or more, more preferably 10% or more, still morepreferably 12% or more, can produce a nonwoven fabric having asufficient strength for practical use. Thermal bonding with the rollpair so as to provide a bonding area of 40% or less, more preferably 30%or less, still more preferably 20% or less, can prevent the resultingnonwoven fabric from being formed into a film-like shape that hardly hasthe advantages of a nonwoven fabric, such as air permeability. Whenthermal bonding is performed with a pair of upper and lower rolls eachhaving raised and recessed portions, the bonding area herein refers tothe ratio of the area where the nonwoven web is in contact with both ofthe raised portions of the upper roll and the raised portions of thelower roll, relative to the total area of the nonwoven fabric. Whenthermal bonding is performed with a pair of a roll having raised andrecessed portions and a flat roll, the bonding area herein refers to theratio of the area where the nonwoven web is in contact with the raisedportions of the roll having raised and recessed portions, relative tothe total area of the nonwoven fabric.

When the nonwoven fabric is mechanically entangled by needle punching,the shape of the needles and the number of needles per unit area can beappropriately selected and adjusted to perform the entanglement. Inparticular, the number of needles per unit area is preferably at least100 per cm² or more in view of the strength and the retention of theshape of the needles. Preferably, a silicone-based oil agent is sprayedon the nonwoven web before needle punching to prevent cutting of thefibers with the needles and to enhance the entanglement of the fibers.

When the mechanical entanglement is performed by water jet punching,columnar jets of water is preferably used. Usually, for creatingcolumnar jets of water, a method in which water is forced out of nozzles0.05 to 3.0 mm in diameter at a pressure of 1 to 60 MPa is suitablyused. For achieving efficient entanglement and consolidation of thenonwoven web, the nonwoven web is preferably treated, at least once, ata pressure of 10 MPa or more, more preferably 15 MPa or more.

For the purpose of improving transportability and controlling thethickness of the nonwoven fabric, the nonwoven web before thermalbonding or mechanical entanglement can be temporarily bonded withcalender rolls at 70 to 170° C. and at a linear pressure of 50 to 700N/cm. The calender rolls may be a combination of upper and lowermetallic rolls or of a metallic roll with a resin or paper roll.

Furthermore, for the purpose of improving the thermal stability, thenonwoven web before thermal bonding or before or after mechanicalentanglement or the nonwoven fabric can be heat treated under strainusing a pin tenter, a clip tenter, or the like, or heat treated withoutstrain (under a strain-free condition) using a hot air dryer or thelike. The temperature for the heat treatment is preferably in the rangeof from the crystallization temperature to the melting point of the PPSfiber that forms the nonwoven web or nonwoven fabric.

EXAMPLES Measurement Methods

(1) Melt Flow Rate (MFR) (g/10 min)

The MFR of PPS was measured in accordance with ASTM D1238-70 under theconditions of a measurement temperature of 315.5° C. and a measurementload of 5 kg.

(2) Average Single Fiber Fineness (dtex)

Ten pieces of small samples were randomly taken from a nonwoven webcollected on a net. The surfaces of the samples were photographed at amagnification of 500 to 1000 times under a microscope. The widths of tenfibers out of each sample, 100 fibers in total, were measured and theaverage values were calculated. The fibers are regarded as fibers havinga circular cross section, and therefore the average width values of thesingle fibers were regarded as the average diameter thereof. From theaverage width values, the weights of the single fibers for each 10,000 min length were calculated based on the solid density of the resin usedand rounded off to the first decimal place to determine average singlefiber finenesses.

(3) Spinning Speed (m/min)

The spinning speed was calculated based on the following formula usingthe average single fiber fineness (dtex) of a fiber and the dischargerate of the resin per hole of a spinneret having various settings(hereinafter abbreviated to discharge rate per hole) (g/min).

Spinning speed=(10000×discharge rate per hole)/average single fiberfineness

(4) Crystallinity (%)

Three samples were randomly taken from fibers after drawing. The sampleswere subjected to measurement with a differential scanning calorimetry(Q1000, made by TA Instruments, Inc.) under the following conditions.The crystallinity of each sample was then determined by the followingformula and the average value thereof was calculated. In the formula,the term “exothermic heat of cold crystallization” refers to theexothermic peak area resulting from cold crystallization, and the term“endothermic heat of fusion” refers to the endothermic peak arearesulting from fusion. The baseline for the calculation of the heat(peak area) was a straight line connecting the heat flow curve in theliquid phase after the glass transition of the amorphous phase and theheat flow curve in the liquid phase after crystal fusion. The baselineintersects the DSC curve and separates the exothermic side from theendothermic side. The heat of fusion of a perfect crystal was 146.2 J/g.

-   -   Measurement atmosphere: nitrogen flow (50 ml/min)    -   Temperature range: 0 to 350° C.    -   Heating rate: 10° C./min    -   Amount of sample: 5 mg

Crystallinity={[(endothermic heat of fusion [J/g])−(exothermic heat ofcold crystallization [J/g])]/146.2 [J/g]}×100

(5) Mobile Amorphous Fraction (%)

Three samples were randomly taken from fibers after drawing. The sampleswere subjected to measurement with a temperature modulated DSC (Q1000,made by TA Instruments, Inc.) under the following conditions. The mobileamorphous fraction in each sample was determined by the followingformula and the average value thereof was calculated. The specific heatof a perfect amorphous solid was 0.2699 J/g.° C.

-   -   Measurement atmosphere: nitrogen flow (50 ml/min)    -   Temperature range: 60 to 200° C.    -   Heating rate: 2° C./min    -   Amount of the sample: 5 mg

Mobile amorphous fraction [%]=(change in specific heat between beforeand after glass transition temperature [J/g.° C.])/0.2699 [J/g.° C.]×100

(6) Rigid Amorphous Fraction (%)

From the crystallinity determined in the above (5) and the mobileamorphous fraction determined in the above (6), the rigid amorphousfraction was calculated by the following formula:

Rigid amorphous fraction [%]=100 [%]−crystallinity [%]−mobile amorphousfraction [%].

(7) Boiling Water Shrinkage (%)

The fibers after drawing were randomly taken out, and five fibers werealigned parallel to each other to give one sample (length: about 10 cm).A load as described below was applied to the sample and the length (L0)was measured. Then, the sample was immersed in boiling water in astrain-free state for 20 minutes, taken out from the boiling water, andallowed to dry. The same load as above was applied to the sample againand the length (L1) was measured. From the lengths L0 and L1, theboiling water shrinkage was calculated and the average value of foursamples was determined. The formulas for calculating the load and theboiling water shrinkage are shown below. The load was rounded off to thesecond decimal place.

Load (g)=0.9×discharge rate per hole (g/min)

Boiling water shrinkage (%)={(L0−L1)/L0}×100

(8) Mass Per Unit Area (g/m²) of Nonwoven Fabric

In accordance with 6.2 “Mass per unit area (ISO method)” in JIS L 1913:2010 “Test methods for nonwovens”, three test pieces having a size of 20cm×25 cm were taken per meter in width from each sample, the masses (g)of the test pieces in standard conditions were measured, and the averagevalue thereof was expressed in terms of mass per m² (g/m²).

(9) Tensile Strength of Nonwoven Fabric

In accordance with 6.3.1 “In standard conditions” of 6.3 “Tensilestrength and elongation rate (ISO method)” in JIS L 1913: 2010 “Testmethods for nonwovens”, tensile test was performed at three points inthe longitudinal direction of a sample under the conditions of a samplesize of 5 cm×30 cm, a holding interval of 20 cm, and a tensile rate of10 cm/min. The average value of the strengths at which the samples brokewas determined as a longitudinal tensile strength (N/5 cm) and roundedoff to the whole number.

(10) Thermal Shrinkage Rate (%) of Nonwoven Fabric

In accordance with 6.10.3 “Dimensional change rate under dry heatconditions” of 6.10 “Dimensional change rate (JIS method)” in JIS L1913: 2010 “Test methods for nonwovens”, the measurement was performed.The temperature inside a constant temperature dryer was 200° C. and heattreatment was performed for 10 minutes.

(11) Heat-Exposure Resistance Test and Longitudinal Tensile StrengthRetention Rate

Several necessary quantity of longitudinal samples having a size of 30cm in length and 5 cm in width were placed in a hot air oven (TABAISAFETY OVEN SHPS-222, made by ESPEC Corp.) and exposed to hot air at210° C. for 1500 hours at an air circulation rate of 300 L/min. Thetensile strengths of the samples before and after the heat-exposureresistance test were measured by the method described in the above (9),and the longitudinal tensile strength retention rates were calculated bythe following formula:

Longitudinal tensile strength retention rate (%)={longitudinal tensilestrength (N/5 cm) after heat-exposure resistance test/longitudinaltensile strength (N/5 cm) before heat-exposure resistance test}×100.

Example 1 PPS Resin

A 100 mol % linear polyphenylene sulfide resin that was intentionallynot copolymerized with trichlorobenzene (made by Toray Industries, Inc.,Product No. E2280, MFR: 160 g/10 min) was dried in a nitrogen atmosphereat 160° C. for 10 hours, and used in the following procedure.

Spinning and Forming into Nonwoven Web

The PPS resin was molten in an extruder, and spun from a rectangularspinneret having a hole diameter of 0.50 mm at a spinning temperature of320° C. and at a discharge rate per hole of 1.38 g/min. The spunfilamentary streams were allowed to cool down and solidify between therectangular spinneret and a rectangular ejector at a distance of 55 cmin an atmosphere at room temperature (20° C.). The filamentary streamsthat had cooled down and solidified were passed through the rectangularejector and were pulled and drawn by compressed air that was heated to230° C. with an air heater and blown out from the ejector at an ejectorpressure of 0.15 MPa. The filaments were collected on a moving net toform a nonwoven web.

The obtained filaments had an average single fiber fineness of 2.8 dtex,a crystallinity of 18.4%, the sum of the rigid amorphous fraction andthe crystallinity of 38.2%, and a boiling water shrinkage of 2.3%. Thespinning speed was 4,998 m/min. During the one-hour spinning, theoccurrence of the breakage of the filaments was zero and thus goodspinnability was observed.

Temporary Bonding and Thermal Bonding

Next, the obtained nonwoven web was temporarily bonded at a linearpressure of 200 N/cm and a temporary bonding temperature of 100° C. witha pair of upper and lower metallic calender rolls installed in theproduction line. The nonwoven fabric was then thermally bonded at alinear pressure of 1000 N/cm and a thermal bonding temperature of 270°C. with a roll pair for embossing which provides a bonding area of 12%and which is composed of an upper metallic embossing roll engraved witha polka dot pattern and a lower metallic roll having a flat surface.Thus, a filament nonwoven fabric of Example 1 was obtained.

The obtained nonwoven fabric had no significant shrinkage in width dueto thermal shrinkage by thermal bonding with the embossing roll pair andshowed good quality without wrinkles. The obtained filament nonwovenfabric had a mass per unit area of 248 g/m², a longitudinal tensilestrength of 434 N/5 cm, thermal shrinkage rates of 0.0% in thelongitudinal direction and 0.1% in the transverse direction, and alongitudinal tensile strength retention rate of 99%.

Example 2

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1 except that the temperature ofthe compressed air was 200° C.

The obtained filaments had an average single fiber fineness of 2.8 dtex,a crystallinity of 17.3%, the sum of the rigid amorphous fraction andthe crystallinity of 37.3%, and a boiling water shrinkage of 7.0%. Thespinning speed was 4,991 m/min. During the one-hour spinning, theoccurrence of the breakage of the filaments was zero and thus goodspinnability was observed.

Temporary Bonding and Thermal Bonding

Next, the nonwoven web was temporarily bonded and then thermally bondedin the same manner as in Example 1 to produce a filament nonwoven fabricof Example 2.

The obtained nonwoven fabric had no significant shrinkage in width dueto thermal shrinkage by thermal bonding with the embossing roll pair andshowed good quality without wrinkles. The obtained filament nonwovenfabric had a mass per unit area of 253 g/m², a longitudinal tensilestrength of 454 N/5 cm, thermal shrinkage rates of 0.1% in thelongitudinal direction and 0.2% in the transverse direction, and alongitudinal tensile strength retention rate of 99%.

Example 3

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1 except that the temperature ofthe compressed air was 140° C.

The obtained filaments had an average single fiber fineness of 2.9 dtex,a crystallinity of 15.1%, the sum of the rigid amorphous fraction andthe crystallinity of 31.3%, and a boiling water shrinkage of 17.5%. Thespinning speed was 4,824 m/min. During the one-hour spinning, theoccurrence of the breakage of the filaments was zero and thus goodspinnability was observed.

Temporary Bonding and Thermal Bonding

Next, the nonwoven web was temporarily bonded and then thermally bondedin the same manner as in Example 1 to produce a filament nonwoven fabricof Example 3.

The obtained nonwoven fabric had no significant shrinkage in width dueto thermal shrinkage by thermal press-bonding with the embossing rollpair and showed good quality without wrinkles. The obtained filamentnonwoven fabric had a mass per unit area of 245 g/m², a longitudinaltensile strength of 472 N/5 cm, thermal shrinkage rates of 0.0% in thelongitudinal direction and 0.1% in the transverse direction, and alongitudinal tensile strength retention rate of 99%.

Example 4

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1 except that the temperature ofthe compressed air was 200° C. and that the ejector pressure was 0.21MPa.

The obtained filaments had an average single fiber fineness of 2.4 dtex,a crystallinity of 24.1%, the sum of the rigid amorphous fraction andthe crystallinity of 49.2%, and a boiling water shrinkage of 2.2%. Thespinning speed was 5,663 m/min. During the one-hour spinning, theoccurrence of the breakage of the filaments was zero and thus goodspinnability was observed.

Temporary Bonding and Thermal Bonding

Next, the nonwoven web was temporarily bonded and then thermally bondedin the same manner as in Example 1 to produce a filament nonwoven fabricof Example 4.

The obtained nonwoven fabric had no significant shrinkage in width dueto thermal shrinkage by thermal press-bonding with the embossing rollpair and showed good quality without wrinkles. The obtained filamentnonwoven fabric had a mass per unit area of 256 g/m², a longitudinaltensile strength of 421 N/5 cm, thermal shrinkage rates of 0.0% in thelongitudinal direction and 0.1% in the transverse direction, and alongitudinal tensile strength retention rate of 98%.

Example 5

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1 except that the temperature ofthe compressed air was 200° C. and that the ejector pressure was 0.25MPa.

The obtained filaments had an average single fiber fineness of 2.2 dtex,a crystallinity of 33.0%, the sum of the rigid amorphous fraction andthe crystallinity of 67.4%, and a boiling water shrinkage of 2.0%. Thespinning speed was 6,198 m/min. In terms of spinnability, during theone-hour spinning, the breakage of the filaments was observed twice.

Temporary Bonding and Thermal Bonding

Next, the nonwoven web was temporarily bonded and then thermally bondedin the same manner as in Example 1 to produce a filament nonwoven fabricof Example 5.

The obtained nonwoven fabric had no significant shrinkage in width dueto thermal shrinkage by thermal press-bonding with the embossing rollpair and showed good quality without wrinkles. The obtained filamentnonwoven fabric had a mass per unit area of 254 g/m², a longitudinaltensile strength of 245 N/5 cm, thermal shrinkage rates of 0.0% in thelongitudinal direction and 0.1% in the transverse direction, and alongitudinal tensile strength retention rate of 99%.

Example 6

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1.

Temporary Bonding and Needle Punching

Next, the nonwoven web was temporarily bonded in the same manner as inExample 1. An oil agent (SM7060: made by Dow Corning Toray Silicone Co.,Ltd.) in an amount of 2% by weight relative to the weight of the fiberswas applied to the nonwoven web. The nonwoven web was entangled byneedle punching at a density of 300 needles/cm² with a needle having onebarb and a barb depth of 0.06 mm to produce a filament nonwoven fabricof Example 6.

The obtained filament nonwoven fabric had a mass per unit area of 301g/m², a longitudinal tensile strength of 490 N/5 cm, thermal shrinkagerates of 1.6% in the longitudinal direction and 1.8% in the transversedirection, and a longitudinal tensile strength retention rate of 99%.

Example 7

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1.

Temporary Bonding and Water Jet Punching

Next, the nonwoven web was temporarily bonded in the same manner as inExample 1. The front and back surfaces of the nonwoven web werealternately entangled at a pressure of 15 MPa with a water jet punching(WJP) machine having nozzles with a diameter of 0.10 mm and a pitch of0.1 mm. The entangled nonwoven web was dried with a hot air dryer whosetemperature was set at 100° C. to produce a filament nonwoven fabric ofExample 7.

The obtained filament nonwoven fabric had a mass per unit area of 285g/m², a longitudinal tensile strength of 462 N/5 cm, thermal shrinkagerates of 1.4% in the longitudinal direction and 1.7% in the transversedirection, and a longitudinal tensile strength retention rate of 99%.

Comparative Example 1

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1 except that the compressed airwas at normal temperature (30° C.) and that the ejector pressure was0.15 MPa.

The obtained filaments had an average single fiber fineness of 3.1 dtex,a crystallinity of 8.9%, the sum of the rigid amorphous fraction and thecrystallinity of 10.7%, and a boiling water shrinkage of 61.2%. Thespinning speed was 4,435 m/min. During the one-hour spinning, theoccurrence of the breakage of the filaments was zero and thus goodspinnability was observed.

Temporary Bonding and Thermal Bonding

Next, temporary bonding and subsequent thermal bonding of the nonwovenweb were attempted in the same manner as in Example 1. However,significant shrinkage in width was observed in the nonwoven web due tothermal shrinkage during thermal bonding with the embossing roll pairand the nonwoven web shrunk and hardened, and thus embossing wasimpossible to perform.

Comparative Example 2

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1 except that the compressed airwas at normal temperature (30° C.) and that the ejector pressure was0.20 MPa.

The obtained filaments had an average single fiber fineness of 2.6 dtex,a crystallinity of 18.2%, the sum of the rigid amorphous fraction andthe crystallinity of 25.3%, and a boiling water shrinkage of 28.5%. Thespinning speed was 5,331 m/min. During the one-hour spinning, theoccurrence of the breakage of the filaments was zero and thus goodspinnability was observed.

Temporary Bonding and Thermal Bonding

Next, temporary bonding and subsequent thermal bonding of the nonwovenweb were attempted in the same manner as in Example 1. However,significant shrinkage in width was observed in the nonwoven web due tothermal shrinkage during thermal bonding with the embossing roll pairand the nonwoven web shrunk and hardened, and thus embossing wasimpossible to perform.

Comparative Example 3

PPS Resin, Spinning, and Forming into Nonwoven Web

The same PPS resin as in Example 1 was spun and formed into a nonwovenweb in the same manner as in Example 1 except that the temperature ofthe compressed air was 230° C. and that the ejector pressure was 0.10MPa.

The obtained filaments had an average single fiber fineness of 4.9 dtex,a crystallinity of 9.4%, the sum of the rigid amorphous fraction and thecrystallinity of 26.8%, and a boiling water shrinkage of 25.0%. Thespinning speed was 2,794 m/min. During the one-hour spinning, theoccurrence of the breakage of the filaments was zero and thus goodspinnability was observed.

Temporary Bonding and Needle Punching

Next, the nonwoven web was temporarily bonded in the same manner as inExample 1 and then needle punched in the same manner as in Example 6 toproduce a filament nonwoven fabric of Comparative Example 3.

However, the thermal shrinkage rates of the obtained filament nonwovenfabric were significantly high and were 21.2% in the longitudinaldirection and 23.4% in the transverse direction. Moreover, the surfacesof the nonwoven fabric after the heat treatment became wrinkled andirregular. The filament nonwoven fabric had a mass per unit area of 295g/m² and a longitudinal tensile strength of 472 N/5 cm. Theheat-exposure resistance test could not be performed because of thesignificant thermal shrinkage.

The production and processing conditions and the measurement results ofthe physical properties and the like in the above Examples andComparative Examples are shown in Table 1.

TABLE 1 Compa- Compa- Compa- Exam- Exam- Exam- Exam- Exam- Exam- Exam-rable rable rable ple ple ple ple ple ple ple Exam- Exam- Exam- 1 2 3 45 6 7 ple 1 ple 2 ple 3 PPS resin MFR g/10 min 160 160 160 160 160 160160 160 160 160 Spinning Spinning temperature ° C. 320 320 320 320 320320 320 320 320 320 Hole diameter of mm ø0.5 ø0.5 ø0.5 ø0.5 ø0.5 ø0.5ø0.5 ø0.5 ø0.5 ø0.5 spinneret Discharge rate per g/min 1.38 1.38 1.381.38 1.38 1.38 1.38 1.38 1.38 1.38 spinneret hole Temperature of ° C.230 200 140 200 200 230 230 Normal Normal 230 compressed air temper-temper- ature ature (30) (30) Fineness dtex 2.8 2.8 2.9 2.4 2.2 2.8 2.83.1 2.6 4.9 Spinning speed m/min 4998 4991 4824 5663 6198 4998 4998 44355331 2794 Crystallinity % 18.4 17.3 15.1 24.1 33.0 18.4 18.4 8.9 18.29.4 Mobile amorphous % 61.8 62.7 68.7 50.8 32.6 61.8 61.8 89.3 74.7 73.2fraction Rigid amorphous % 19.8 20.0 16.2 25.1 34.4 19.8 19.8 1.8 7.117.4 fraction Crystallinity + rigid % 38.2 37.3 31.3 49.2 67.4 38.2 38.210.7 25.3 26.8 amorphous fraction Boiling water shrinkage % 2.3 7.0 17.52.2 2.0 2.3 2.3 61.2 28.5 25.0 Number in FIGS. 1 — (1) (2) (3) (4) (5)(1) (1) (6) (7) (8) and 2 Temporary Temperature ° C. 100 100 100 100 100100 100 100 100 100 bonding by Linear pressure N/cm 200 200 200 200 200200 200 200 200 200 calendering Thermal Temperature ° C. 270 270 270 270270 — — 270 270 — bonding Linear pressure N/cm 1000 1000 1000 1000 1000— — 1000 1000 — Needle Number of needles needles/cm² — — — — — 300 — — —300 punching Water jet Pressure MPa — — — — — — 15 — — — punchingNonwoven Mass per unit area g/m² 248 253 245 256 254 301 285 — — 295fabric Tensile strength N/5 cm 434 454 472 421 245 490 462 — — 472(longitudinal) Thermal Longitudinal % 0 0.1 0 0 0 1.6 1.4 — — 21.2shrinkage Transverse % 0.1 0.2 0.1 0.1 0.1 1.8 1.7 — — 23.4 rateLongitudinal tensile % 99 99 99 98 99 99 99 — — — strength retentionrate

As shown in Table 1, the PPS fibers in Examples 1 to 5 having the sum ofthe crystallinity and the rigid amorphous fraction of 31.3 to 67.4%could be thermally bonded with the embossing roll pair and moreoverthermal shrinkage at 200° C. was hardly observed, indicating excellentthermal dimensional stability. Especially, the fibers of Examples 1 to 4having the crystallinity of 15.1 to 24.1% were excellent in thermalbonding properties and the resulting fabrics had excellent mechanicalstrength.

For the filament nonwoven fabrics of Examples 6 and 7 obtained bymechanically entangling the nonwoven web having the sum of thecrystallinity and the rigid amorphous fraction of 38.2% by needlepunching or water jet punching, thermal shrinkage at 200° C. was hardlyobserved, and the fabrics had excellent thermal dimensional stability.

In contrast, the fabrics of Comparative Examples 1 and 2 having the sumof the crystallinity and the rigid amorphous fraction of 10.7% and25.3%, respectively, had high boiling water shrinkage rates.Consequently, significant shrinkage in width was observed in thenonwoven webs due to thermal shrinkage during the thermal bonding andthe nonwoven webs shrunk and hardened, and thus embossing was impossibleto perform. In Comparative Example 3 in which the nonwoven web had thesum of the crystallinity and the rigid amorphous fraction of 26.8%, thefilament nonwoven fabric obtained by mechanical entangling the nonwovenweb by needle punching had significant thermal shrinkage at 200° C. andwas not suitable for practical use.

The polyphenylene sulfide fiber and the nonwoven fabric comprising thefiber described in the above embodiments and Examples are illustrated todemonstrate the technical ideas of the present invention. Thecomposition of the resin, the spinning and drawing conditions, thenonwoven web forming conditions, the single fiber fineness, thecrystallinity, the rigid amorphous fraction, and the like are notlimited to those in the above embodiments and Examples and can bemodified in various ways within the scope of the claims of the presentinvention.

For example, in the above Examples, the case in which a nonwoven web isformed by spun bonding has been described. In the present invention,however, the nonwoven web may be formed by other methods. Needless tosay, the type of the PPS resin to be used is not limited to those in theabove Examples.

The nonwoven fabric comprising the polyphenylene sulfide fiber of thepresent invention has excellent mechanical strength while maintainingthe properties of a PPS resin, namely, heat resistance, chemicalresistance, and flame retardancy. Therefore, the nonwoven fabric isuseful for various industrial applications including heat-resistantfilters, electrical insulation materials, and battery separators.

1. A polyphenylene sulfide fiber comprising polyphenylene sulfide as amain component and having the sum of the crystallinity and the rigidamorphous fraction of 30% to 90%.
 2. The polyphenylene sulfide fiberaccording to claim 1, wherein the crystallinity is not less than 5% andless than 25%.
 3. A nonwoven fabric comprising the polyphenylene sulfidefiber according to claim
 1. 4. The nonwoven fabric according to claim 3,which is produced by consolidation by thermal bonding or mechanicalentanglement.